/*** 自定義 ID 生成器* ID 生成規則: ID長達 64 bits** | 41 bits: Timestamp (毫秒) | 3 bits: 區域（機房） | 10 bits: 機器編號 | 10 bits: 序列號 |*/public class GameUUID{// 基準時間private long twepoch = 1288834974657L; //Thu, 04 Nov 2010 01:42:54 GMT// 區域標志位數private final static long regionIdBits = 3L;// 機器標識位數private final static long workerIdBits = 10L;// 序列號識位數private final static long sequenceBits = 10L;// 區域標志ID最大值private final static long maxRegionId = -1L ^ (-1L << regionIdBits);// 機器ID最大值private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);// 序列號ID最大值private final static long sequenceMask = -1L ^ (-1L << sequenceBits);// 機器ID偏左移10位private final static long workerIdShift = sequenceBits;// 業務ID偏左移20位private final static long regionIdShift = sequenceBits + workerIdBits;// 時間毫秒左移23位private final static long timestampLeftShift = sequenceBits + workerIdBits + regionIdBits;private static long lastTimestamp = -1L;private long sequence = 0L;private final long workerId;private final long regionId;public GameUUID(long workerId, long regionId) {// 如果超出范圍就拋出異常if (workerId > maxWorkerId || workerId < 0) {throw new IllegalArgumentException("worker Id can't be greater than %d or less than 0");}if (regionId > maxRegionId || regionId < 0) {throw new IllegalArgumentException("datacenter Id can't be greater than %d or less than 0");}this.workerId = workerId;this.regionId = regionId;}public GameUUID(long workerId) {// 如果超出范圍就拋出異常if (workerId > maxWorkerId || workerId < 0) {throw new IllegalArgumentException("worker Id can't be greater than %d or less than 0");}this.workerId = workerId;this.regionId = 0;}public long generate() {return this.nextId(false, 0);}/*** 實際產生代碼的** @param isPadding* @param busId* @return*/private synchronized long nextId(boolean isPadding, long busId) {long timestamp = timeGen();long paddingnum = regionId;if (isPadding) {paddingnum = busId;}if (timestamp < lastTimestamp) {try {throw new Exception("Clock moved backwards. Refusing to generate id for " + (lastTimestamp - timestamp) + " milliseconds");} catch (Exception e) {e.printStackTrace();}}//如果上次生成時間和當前時間相同,在同一毫秒內if (lastTimestamp == timestamp) {//sequence自增，因為sequence只有10bit，所以和sequenceMask相與一下，去掉高位sequence = (sequence + 1) & sequenceMask;//判斷是否溢出,也就是每毫秒內超過1024，當為1024時，與sequenceMask相與，sequence就等于0if (sequence == 0) {//自旋等待到下一毫秒timestamp = tailNextMillis(lastTimestamp);}} else {// 如果和上次生成時間不同,重置sequence，就是下一毫秒開始，sequence計數重新從0開始累加,// 為了保證尾數隨機性更大一些,最后一位設置一個隨機數sequence = new SecureRandom().nextInt(10);}lastTimestamp = timestamp;return ((timestamp - twepoch) << timestampLeftShift) | (paddingnum << regionIdShift) | (workerId << workerIdShift) | sequence;}// 防止產生的時間比之前的時間還要小（由于NTP回撥等問題）,保持增量的趨勢.private long tailNextMillis(final long lastTimestamp) {long timestamp = this.timeGen();while (timestamp <= lastTimestamp) {timestamp = this.timeGen();}return timestamp;}// 獲取當前的時間戳protected long timeGen() {return System.currentTimeMillis();}}